How do they learn this?

Charlie is so lucky to have his Grammy and Pa Morgan close by. He spends every other Friday with them and gets so excited when they come to our house to pick him up. It's comforting for me to know that he's getting the best care and attention while I'm at work and we can't thank them enough for all they do for us and for spending quality time with Charlie. This past Friday, the Grandparents informed me that Charlie learned something new and they were able to catch it on camera. I was so excited to learn what this new skill was until they showed me. Wow...both nostrils! How and where did Charlie learn to pick his nose? I guess he was doing it all day long and really enjoying it. I haven't yet seen the action live, but I'm looking out for it.